The role of Clostridium difficile spore surface proteins in mammalian cell interactions

Abstract

Clostridium difficile (C. difficile) is a Gram positive, anaerobic spore-forming bacterium, which is estimated to be responsible for about one-quarter of all hospital acquired infections. C. difficile is the main cause of pseudomembranous colitis (PMC) and antibiotic associated colitis and diarrhoea known as C. difficile associated disease (CDAD). CDAD is difficult to treat and contain due to the ability of C. difficile to form robust spores that can persist and be easily transferred from one individual to another in a hospital environment. More than 90% of C. difficile infection (CDI) occurs after or during antibiotic treatment. Antibiotics act by disrupting the normal colonic flora allowing the germinating C. difficile spore to outgrow and colonize the host’s intestinal tract. During the course of CDI, C. difficile undergoes sporulation and releases spores to the colonic environment. The elevated relapse rates of CDI suggest that C. difficile spores has mechanisms to efficiently persist in the host colonic environment however little is known about the role of proteins in the outermost layer of the spore has to play in persistence.This thesis investigates the role of the spore surface proteins in mammalian cell interactions. Results suggest that the spore coat protein CotE could have a role to play in the adherence of the spore to intestinal epithelial cells and mucus. The BclA protein may have a similar role to that of BclA in Bacillus anthracis (B. anthracis) where BclA has been shown to promote tropism towards macrophages and a reduction in adherence to lung epithelial cells. Little is known about the interaction of the C. difficile spore and innate immune cells, therefore the interaction of C. difficile spores with the murine macrophage cell line J774.1 has been examined. Results suggest that BclA may act as a Pathogen Associated Molecular Pattern (PAMP) which is recognized by Pattern Recognition Receptors (PRRs) of macrophages leading to efficient phagocytosis of the C. difficile spore. Spores are able to remain dormant and are able to survive within macrophages and produce cytotoxic effects to J774.1 cells. Persistence of C. difficile in the host might be mediated through the adherence of spores to the host’s intestinal epithelium and surviving attacks of phagocytic cells. Investigating mechanisms of persistence of the spore in the host is of great importance in understanding the pathogenesis of CDI and will lead to effective diagnosis, treatment and prevention of the infection. <br/